Sunlight control glasses are commonly used in applications such as building glass windows and vehicle windows, typically offering high visible transmission and low emissivity. High visible transmission can allow more sunlight to pass through the glass windows, thus being desirable in many window applications. Low emissivity can block infrared (IR) radiation to reduce undesirable interior heating.
In low emissivity glasses, IR radiation is mostly reflected with minimum absorption and emission, thus reducing the heat transferred to and from the low emissivity surface. Typical sunlight control glasses generally have an emissivity of about 0.1 and a light transmission of about 80%. High transmittance, low emissivity glasses generally include a reflective metal film (e.g., silver) to provide infrared reflectance and low emissivity, along with various dielectric layers, such as tin oxide or zinc oxide, to provide a barrier to prevent oxidation or corrosion, as well as to act as optical fillers and function as anti-reflective coating layers to improve the optical characteristics of the glass panel.
In certain cases, the glasses are heat treated for tempering, bending or strengthening, requiring the use of temperatures of 500 C or higher. The heat treatment process can affect the coatings, such as deterioration, structural or color changes, or become hazy following the heat treatment, exhibiting a reduction in visible transmission and significant color changes.